My invention comprises improvements in a multiple speed ratio planetary gear transmission such as that shown in U.S. Pat. No. 4,347,765, which is assigned to the assignee of this invention. It is an improvement also in the transmission shown in U.S. Pat. No. 3,486,398. The transmission described in the '765 patent includes a Ravagineaux gear set together with clutches and brakes for establishing each of four forward driving ratios. The highest speed ratio is an overdrive. Overdrive is achieved by anchoring one of the sun gears of the Ravagineaux gear set of larger pitch diameter by means of an overdrive brake band. A direct drive clutch, which connects the torque input shaft or the engine crankshaft to the carrier of the Ravagineaux gear set, is engaged thereby overspeeding the carrier of the gear set. The carrier is connected to the output shaft.
When the direct drive clutch is applied while torque is being distributed to the larger diameter sun gear of the planetary gear set, a split torque delivery is achieved. A portion of the torque is distributed fully mechanically through the direct clutch and the balance being distributed hydrokinetically through the torque converter and through one of the selectively engageable clutches to the larger pitch diameter sun gear. This split torque delivery reduces hydrokinetic losses while retaining a large degree of the cushioning effect of the converter, thus eliminating sharp torque fluctuations in the driveline.
The split torque arrangement, and the open converter option described previously, can be applied to a transmission having the gear characteristics shown in U.S. Pat. No. 4,509,389, which is assigned to the the assignee of this invention. The '389 patent describes a transaxle transmission in which the planetary gearing is located concentrically with respect to the output shaft axis and in spaced parallel disposition with respect to the engine crankshaft axis. The converter of the transaxle of the '389 patent is disposed between the engine and the driving sprocket of a chain transfer drive and is concentrically arranged with respect to the engine crankshaft. The transfer drive distributes torque from the turbine of the converter to the torque input clutches arranged about the axis of the output shaft.
I have made provision in my improved construction for a clutch arrangement for a planetary hydrokinetic torque converter transmission that will provide, at the option of the operator, a fully open converter in each of four forward driving ratios but which will permit the operator to select during operation in the higher speed ratios either a partial hydrokinetic torque delivery or a full mechanical torque delivery to the input elements of the gearing depending upon whether a normal drive mode, an economy mode or light throttle drive mode is desired. The operator has a choice of selecting a normal drive mode, an advanced throttle mode or an economy or light throttle drive mode. The choice of a particular drive mode depends upon the engagement or release of the additional clutch element that is introduced in a strategic fashion in the clutch and brake arrangement.